net: bcmgenet: use napi_complete_done return value

net: bcmgenet: use napi_complete_done return value

Make use of the return value from napi_complete_done(). This allows users to
use the gro_flush_timeout and napi_defer_hard_irqs sysfs attributes for
configuring software interrupt coalescing.

Signed-off-by: Zak Kemble <zakkemble@gmail.com>
Tested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250610220403.935-2-zakkemble@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>